AN0873 using the MCP2515 CAN developer’s kit

There are several windows associated with the Register template: MCP2515 EVALUATION BOARD WINDOW This window displays the connection status, parallel port address and MCP2515 mode of ope

M AN873

INTRODUCTION

The MCP2515 eases software development and

shortens the learning curve for the MCP2515 by

providing three PC software templates with different

functions that CAN node designers can use as needed

By using one of the templates, the user can read,

display, and modify all of the registers in the MCP2515

down to the bit level Another template can

demonstrate basic input/output functionality by

allowing messages to be transmitted and received on

the CAN bus Finally, the third template is a

demonstration template that, by using a

preprogrammed PICmicro® microcontroller (MCU),

implements a two node CAN bus that gets the user “on

the bus” in the shortest amount of time and effort

This application note serves as a three-part tutorial for

the MCP2515 and discusses the three software

templates in detail as well as the important menu items

Figure 1 is a block diagram of the MCP2515 board The

board is a two node CAN system that can be used

together to implement a simple bus or can be

connected to an external bus using the off-board

connector For the purposes of this application note,

the left node will be referred to as the PC node and the right node will be referred to as the PICmicro node.

Both nodes are identical except for the controller interface to the MCP2515 is a PC for one node and a PICmicro controller for the other node By providing a two node CAN network on a single board, a simple CAN network can be implemented with one PCB

PC Node

The left node (as oriented in Figure 1) is referred to as the PC node The PC performs the microcontroller functions and interfaces to the MCP2515 via Serial Peripheral Interface (SPI™) through the parallel port The software templates control this node

PICmicro Node

The right node is referred to as the PICmicro node and represents a typical CAN node This node is used by the end user as needed When running the “MCP2515 Evaluation” template, demonstration firmware is used

to complete a CAN system

Author: Pat Richards

Microchip Technology Inc.

To PC

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SPI™

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PC Node PICmicro ® Node

Using the MCP2515 CAN Developer’s Kit

OVERVIEW OF THE SYSTEM

SOFTWARE

There are three software templates that are used to

control one or both of the nodes on the board This

tutorial will discuss all three of the templates Refer to

the User’s Guide for images of the windows if needed

The following is a brief discussion of the three

templates:

Register Template

The “Register” template is a low-level template that

allows bit-level control of the MCP2515 registers This

template may be used to become familiar with the

MCP2515 by experimenting with mask and filter

settings, bit timings, configuration registers and other

functions associated with configuring the MCP2515

There are several windows associated with the

Register template:

MCP2515 EVALUATION BOARD WINDOW

This window displays the connection status, parallel

port address and MCP2515 mode of operation The

MCP2515 can be reset in this window and MCP2515

register contents be saved and loaded The register

contents are saved as a HEX file

STATUS WINDOW

The status window shows the contents of CANSTAT

register (operation mode and interrupt flag codes), TX

and RX error counts (TEC and REC registers) and

EFLG register contents

In addition, there are buttons to clear the overflow flag

bits in the EFLG register

MESSAGE FILTERS WINDOW

The masks and filters are configurable in this window,

allowing the user to setup and test for message

acceptance The ‘Message Filters’ window allows

messages to be tested against the masks and filters

without physically going on the bus This is

accomplished by entering values in the mask, filters

and test identifier fields and pressing the “Test Buf n”

button

PHYSICAL LAYER WINDOW The three CNF registers used for all CAN bit timings are configured in this window

CONFIGURATION WINDOW TXRTSCTRL, BFPCTRL, CANINTF, CANINTE and CANCTRL are all modified from this window These are the control and flag registers

If a message is received while in the Register template, the receive buffer flags in CANINTF (RX0IF and RX1IF) must be cleared manually to receive additional messages

TRANSMIT WINDOW The transmit window controls the buffer contents for the transmit registers including TXBnCTRL, the identifier registers and the data registers

RECEIVE WINDOW This window contains all of the buffer contents for the receive buffers including RXBnCTRL, the identifier registers and the data registers

Basic Template

This template provides high-level control of one node (PC node) and is identical to the “MCP2515 Evaluation” template, minus the window for the second node (see the tutorial, part 1) This template can be thought of as

a simple bus monitor with transmit capabilities BUS STATUS

This window, labeled ‘MCP2515 CAN Controller’, provides several pieces of information about the status

of the bus including nominal bus loading, status of node (ON or OFF the bus) and bus bit rate

OUTPUT The output window displays the messages that are received and transmitted A time stamp indicates either delta times or absolute times between messages (see

“Message Format Window” description)

HISTORY LIST The history list window is used to collect transmitted messages for saving to a file This file can be opened later and messages can be selected for retransmission Some or all messages can be selected for transmission This window works in conjunction with the ‘’Timed Transmission” window

For the demo program, the history list window is used

to send initial configuration data to the PICmicro® MCU

Note: The templates can be saved as projects

which will save the layout and default

properties by selecting File > Save Saving

the project does not save the register

contents of the MCP2515 Saving the

register contents can be done in the

Register template as discussed at the end

of the Register Template tutorial (Part 3)

Note: The masks and filters cannot be physically

written to the registers unless the

MCP2515 is in “Configuration” mode

Note: The CNF registers can only be modified

while the MCP2515 is in “Configuration” mode

TIMED TRANSMISSIONS

The timed transmissions window is used to send the

messages in the history list The messages can be sent

either one time (one shot) or repeated at regular

inter-vals (cyclic)

MESSAGE FORMAT WINDOW

This window determines the format of the displayed

data in the output window The default is ‘Standard Text

Format’ which displays the message data as normal

data

To change the property of the “Standard Text Format”,

highlight “Standard Text Format” and press the

“Properties” button The numeric base and the time

display can be changed as indicated in Figure 2

OUTPUT WINDOW

MCP2515 Evaluation Template

This template contains a simple demonstration

program Only high-level control is possible on the PC

node Indirect control of the PICmicro node is made

possible via the CAN bus (i.e., the PICmicro node is

configured by the PC node via the CAN bus) The

demo program incorporates the CAN Kingdom Higher

Layer Protocol (HLP) A specific set up procedure

(covered later) is required to enable the two nodes to

communicate with each other

The windows associated with the Evaluation Template

are the same as the Basic template with the following

addition:

MCP2515 EVALUATION BOARD CONTROLS

WINDOW

This window, combined with the “Output” window, is the

main window of interest for the demo This window

displays the graphical representation of the messages

on the CAN bus

UNDERSTANDING THE MENUS

There are several menu items that are discussed in this application note The remaining menu items that are not discussed are the self-explanatory menus, such as

“File > Save” and “Help” The menus change slightly between the three software templates as discussed

Register Template Menus

The menu items for the Register template are shown in Figure 3

The three menus that are discussed are:

VIEW MENU This menu makes visible/invisible, the windows loaded

in the Register Template

MESSAGES MENU This menu loads windows associated with the Register Template

OPTIONS MENU The “Options” menu contains two sub-menu items that,

as the name implies, sets options for the software

Options > Global - as shown in Figure 4 has autosave

options and numeric base settings The numeric base settings select the default numeric base as displayed/ entered in the windows Selecting hexadecimal auto-matically places a ‘$’ in front of the entered number indicating the number entered is HEX

Note: Selecting a window while holding down the

shift key will load a copy of the window so that more than one window of the same type can be visible This is useful for opening multiple “Receive” and “Transmit” windows for viewing multiple buffers simultaneously

FIGURE 4: OPTIONS > GLOBAL

Options > MCP2515 - as shown in Figure 5 sets the

clock frequency, parallel port address, and whether the

MCP2515 is reset on software power-up

The clock frequency and parallel port address must be

set properly for the software to function properly The

MCP2515 clock frequency is used in calculating the

CAN bus rate and is therefore required to be set The

parallel port address much match the BIOS address

setting Typical values for the parallel port are 0x3BC,

0x378, and 0x278 Address 0x378 is the most common

default for LPT1

FIGURE 5: OPTIONS > MCP2515

Basic and Demonstration Template Menus

The Basic and Demonstration Template menus are identical as shown in Figure 3 The sub-menus are same for the Basic and Demonstration templates However, they differ from the Register template sub-menus as follows:

MESSAGES MENU The “Messages” contains two sub menus that select transmit message formats

Messages > Universal > Universal - (shown in

Figure 6) loads a window used for transmitting mes-sages onto the CAN bus The identifier, data length, and data are entered and sent with this window The

“Universal” window can be thought of as a window for sending raw/unformatted messages Other windows under “Messages > Universal” change the formatting of how outgoing messages are entered For example, transmitted messages can be entered as integers, floats, longs or strings by selecting the proper sub-menu

FIGURE 6: MESSAGES > UNIVERSAL

>UNIVERSAL

Messages > CAN Kingdom - this sub menu is for sending CAN Kingdom formatted messages and is beyond the scope of this application note

OPTIONS MENU The “Options” menu is identical to the “Options” menu

in the “Register Template” except for the addition of a

“King’s Pages” sub-menu which is beyond the scope of this application note

TUTORIAL PART 1: SETTING UP AND

RUNNING THE DEMO

The MCP2515 CAN Development Kit demo utilizes

both of its CAN nodes to demonstrate basic CAN

communications Each node is set up to transmit and

receive messages

Initial Set Up

A few initial set up procedures should be performed to

insure proper operation before continuing

VERIFY/SET THE PARALLEL PORT ADDRESS

The parallel port address must match the operating

system BIOS setting To set/verify, select “Options >

MCP2515 ”

SET OSCILLATOR FREQUENCY IN

SOFTWARE

The oscillator frequency must be set to match the

board oscillator so the CAN bit rate will be reflected

accurately To set, select “Options > MCP2515 ” and

set to the proper oscillator frequency (16000 kHz if

using the 16 MHz oscillator supplied with the kit)

SAVE CONFIGURATION

Saving the configuration as a project insures that the

new settings are saved To save, select “File > Save”

and name the project something descriptive

REOPEN SAVED PROJECT

This refreshes the settings to the saved values To

reopen, select “File > Reopen” and choose the file that

was just saved

Running the Demo

Open a new “MCP2515 Evaluation Board” project template (File > New)

Refer to Figure 7 for the configuration procedure After stepping through the configuration procedure, the two nodes should be communicating with each other A receive message (received by the PC node) should be displayed in the “Output” window at every timer interval

as set in the “MCP2515 Evaluation Board Controls” window ($100 or 256 ms in the case of the flow diagram) The data contains the potentiometer value and the S4, S5, S6 button status as read by the PICmicro node

FIGURE 7: DEMO CONFIGURATION PROCEDURE

SetFosc = 16 MHz

Set numeric base to HEX

Set “Display” output to HEX

Set bit rate = 125 kb/s

Go “on-bus”

Send configuration data to

Set transmit rate for PICmicro PICmicro node

node

Communicate

Must set the on-board oscillator value so the bit timing will be calculated properly

(Options > MCP2515)

Sets the default numeric base for entered numbers and places ‘$’ in front of the number

(Options > Global)

Configures the “Output” window display

(Highlight “Standard Text Format” in the “Select Formatters” window and press

“Properties”).

Select the “Bus Parameters” tab in

the “MCP2515 Can Controller”

window and set the bit rate

Select the “Bus Statistics” tab in

the “MCP2515 CAN Controller”

window and press “Go on Bus”

Open “History List” Window

(View > History List)

Load configuration messages

(Press “Load” and select

“mcsetup.hst”)

Send messages to PICmicro node

(Press “Send All”)*

Set “Timer Rate” in the “MCP2515

Evaluation Board Controls” window

to $100 (=> 256 ms)

The PICmicro node should now be sending sensor status (POT and S4, S5, S6 buttons) at 256 ms intervals

* The “Output” window should display some transmitted messages and two received messages If both receive messages are not displayed, reset the nodes by pressing MCLR on the PICmicro node and “Reset Board” button on the PC node and go to the “Go on-bus” step

Two transmit messages can be displayed in the

“Output” window by checking/unchecking the LED

boxes or by pressing the “Set” button to set the transmit

interval time These controls are contained in

the”MCP2515 Evaluation Board Controls” window

The function of each node is explained in more detail

below

PC Node

The PC node is set up to receive and display all

messages sent by the PICmicro node (in the “Output”

window) The received messages contain

potentiometer data and button status (S4, S5, S6) and

are displayed graphically in the “MCP2515 Evaluation

Board Controls” window The “raw” message is

displayed in the “Output” window

The PC node can transmit two message types:

1 The timer rate that the PICmicro node uses to

schedule its message transmissions

2 The digital output of the RXnBF pins, which are

indicated on the associated LEDs These pins

on the MCP2515 are configured as general

purpose outputs for the purpose of the demo

The messages are transmitted by either pressing the

“Set” button or checking/unchecking the LED

checkboxes in the “MCP2515 Evaluation Board

Controls” window (Figure 8)

BOARD CONTROLS

PICmicro Node

The PICmicro node is set up to respond to messages received by the PC node This response will either involve changing it’s own transmit interval or driving the RXnBF pins which are reflected on corresponding LEDs

The PICmicro node will transmit a single message at the predefined transmit interval ($100 ms, or 256 ms for the tutorial) which contains the ADC value from the potentiometer in byte 1 This message also contains the button status for S4, S5, and S6 in byte 0

Message Formats

There are three different message identifiers that are used in the system implementation Each identifier indicates a specific function as explained in Table 1

n - represents changing data

SCHEDULED TRANSMISSION FREQUENCY

(MESSAGE 066)

This message is sent from the PC node when “Set” is

pressed and contains (in DB1 and DB2) the frequency

in which the PICmicro node is to send data The “Timer

Rate” text box sets the transmission frequency The

format of the data is:

• DB2 - eight MSbs of the transmission frequency

• DB1 - the six LSbs of the transmission frequency

Example: if the “Timer Rate” is set to 0xFFFF, the

resulting data in the message would be:

• DB1 = FC, DB2 = FF

This implies that the actual maximum = 0x3FFF =

16,383 => 16.383 seconds

Example: if the “Timer Rate” = 0x100 (256 ms), as in

the flow diagram The resulting data in the message

would be DB1 = 00, DB2 = 40

LED CONTROL (MESSAGE 067)

This message is sent from the PC node and is used to

control the RXBFn LEDs on the PICmicro node

The format of the data is:

• LED RXFB0 - DB0, bit0; (0 = OFF, 1 = ON)

• LED RXFB1 - DB0, bit1, (0 = OFF, 1 = ON)

POTENTIOMETER AND BUTTONS (MESSAGE

069)

This message is scheduled and is sent from the

PICmicro node The message is sent at regular

intervals as determined by message ‘066’ and contains

the digital equivalent of the potentiometer and the

button status for the three buttons associated with the

PICmicro node For each button, there is one bit

showing the current status and one sticky bit that is set

if the button has been pressed since the last poll

The format of the data:

• DB0 - button status (six MSbs => three status bits

and three sticky bits)

• DB1 - analog-to-digital converted value

TUTORIAL PART 2: THE BASIC TEMPLATE

The “Basic” template is identical to the “MCP2515 Evaluation” template in every aspect except that the

“MCP2515 Evaluation Board Controls” is not available

in the “Basic” template Therefore, this tutorial will focus

on the different settings/configurations available

Changing the Output Window

The “Output” window is the main window of activity in the “Basic” template and can be modified to different display properties

SCROLLING AND FIXED MESSAGES The messages can be displayed in either scrolling or fixed format simply by clicking the right mouse button while the cursor is over the “Output” window and selecting the proper display properties (Figure 9)

Scrolling Messages - deselect “Fixed Positions”.

Selecting “Auto Scroll” automatically scrolls the window

to the newest message

Non-scrolling Messages - Select “Fixed Positions”.

This selection anchors messages with matching identifiers into one position; only the data and time are updated

CHANGING THE TIME BASE The “Time” can be displayed as either free-running time between messages or as delta time by highlighting

“Standard Text Format” in the “Select Formatters” window and pressing the “Properties” button (see Figure 2)

WINDOW DISPLAY PROPERTIES

Note: If the Demo Tutorial (Part 1) was set up

prior to this one, the PICmicro node is probably still sending messages at regular intervals Setting the CAN bit rate to

125 kb/s and going on the bus will display these messages in the “output” window

TUTORIAL PART 3: THE REGISTER

TEMPLATE

As described earlier, the “Register” template is a low

level template that allows bit-level control of the

MCP2515 registers This template may be used to

become familiarized with the MCP2515 by

experimenting with mask and filter settings, bit timings,

configuration registers, and other functions associated

with configuring the MCP2515

This tutorial will discuss the associated windows and

provide examples for some In addition, a Loopback

mode demonstration will be given to demonstrate the

basic steps required for successful CAN

communications with the MCP2515

Initial Set Up

A few initial set up procedures should be performed to

insure proper operation before continuing

VERIFY/SET THE PARALLEL PORT ADDRESS

The parallel port address must match the operating

system BIOS setting To set/verify, select “Options >

MCP2515 ”

SET OSCILLATOR FREQUENCY IN

SOFTWARE

The oscillator frequency must be set to match the

board oscillator so the CAN bit rate will be reflected

accurately To set, select “Options > MCP2515 ” and

set to the proper oscillator frequency (16000 kHz if

using the 16 MHz oscillator supplied with the kit)

SAVE CONFIGURATION

Saving the configuration as a project insures that the

new settings are saved To save, select “File > Save”

and name the project something descriptive

REOPEN SAVED PROJECT

This refreshes the settings to the saved values To

reopen, select “File > Reopen” and choose the file that

Mask and Filter Settings

The “MCP2515 Message Filters” window can be used

to experiment with various mask and filter configurations and how these configurations apply to incoming message IDs For example, setting “RXM0”,

“RXF0”, “RXF1”, and “Test Identifier” as shown in Figure 10 would reveal that the Test Identifier would match RXF1 and be accepted into buffer 0 Pressing the “Test Buf n” buttons is a software test of the masks and filters

Refer to the MCP2515 data sheet for more details on mask and filter operations

FILTERS

When finished setting the mask and filters, the MCP2515 can be written by pressing the “Write” button while in “Configuration” mode

IMPORTANT CONSIDERATIONS

• The mask/filter and CNF registers are not written unless the “Write” button is pressed while the MCP2515 is in Configuration mode

• An ‘x’ at the end of a value indicates “extended” identifier (29 bits) If a filter value has an ‘x’, the incoming identifier will be accepted only if it also is extended (contains an ‘x’)

• The’$’ represents HEX

• Standard identifiers are 11-bits with a range of

$0 - $7FF

• Extended identifiers are 29-bits with a range of

$0 - $7FFFFFFE

Note: Unlike the “Basic” and “Evaluation”

templates which modify specific registers

automatically, all registers of the MCP2515

while in the “Register” template are

controlled manually (e.g transmit requests

are set manually and the receive flags

must be cleared manually for each

message sent and received) In essence,

the user is the microcontroller while in the

“Register” template

Bit Timing

The “MCP2515 Physical Layer” window contains the

three CNF registers which are used to set the CAN bit

rate The resulting bit rate is displayed at the bottom of

the window for a given FOSC and CNF register values

FIGURE 11: PHYSICAL LAYER

WINDOW

Example, Figure 11 shows one possible configuration

of the bit timing registers for a CAN bit rate of 125 kb/s

using a 16 Mhz oscillator

Configuration Window

This window contains the configuration registers as

shown in Figure 12 The following examples are

provided to become familiar with the register

operations:

TXRTSCTRL

This register configures the TXnRTS pins as either

request-to-send pins for their associated transmit

buffers or as general purpose inputs

Setting bits 2:0 = b’00’ configures the pins as inputs

The operation of these pins as inputs can be tested by

pressing and holding one or more switches (S1, S2,

S3) and pressing “Read” Bits 5:0 will reflect the status

of the buttons

BFPCTRL

This register configures the two RXnBF pins as receive

buffer full pins, as general purpose outputs, or tri state

(off)

Setting bits 3:2 = b‘11’ and bits 1:0 = b‘00’ configures

the pins as outputs The associated RXBFn LEDs can

be toggled on/off by changing the values of bits 5:4 and

clicking “Write”

CANINTE AND CANINTF CANINTE is the interrupt enable register that routes it’s associated flag bit in CANINTF to the INT pin The flag bits in CANINTF can be set/cleared regardless of CANINTE

To demonstrate the interrupts, simply set a bit in CANINTE and toggle its associated bit in CANINTF The INT pin LED should toggle with the flag bit Example: Set CANINTE.RX0IE = 1 (bit 0) and then toggle CANINTF.RX0IF (bit 0) and click “Write” The INT LED will toggle with the flag bit

CANCTRL The CANCTRL register sets the operation mode and the CLKOUT prescaler

The operation mode can be changed by either selecting the mode from the pull-down menu or by toggling the three MSb

REGISTERS

Status Window

The “MCP2515 Status” window contains the status of several parameters including the mode of operation, pending interrupts, transmit and receive error counters values, and receive buffer overflow status

Transmit and Receive Registers

The transmit and receive registers are displayed in two separate windows and contain the identifier, data length code, and data registers The transmit register window also contains the CTRL (TXBnCTRL) register which contains the Transmit Request (TXREQ) bit (bit 3)

Note: The CNF registers can only be modified

while in “Configuration” mode Any other

mode will gray out the registers indicating

they are read-only